Bug#902924: debootstrap: doesn't mount /proc when building chroot inside LXD container

[Colin Watson <cjwatson@ubuntu.com>]

Package: debootstrap
Version: 1.0.105
Severity: important
User: ubuntu-devel@lists.ubuntu.com
Usertags: origin-ubuntu cosmic

All the automatic builds of Ubuntu live filesystems started failing
today.  I tracked this down to changes in debootstrap 1.0.105.  Here's
how to reproduce it locally:

  $ lxc launch images:debian/sid/amd64 debootstrap-test
  $ lxc exec debootstrap-test -- apt -y install debootstrap
  $ lxc exec debootstrap-test -- debootstrap cosmic /build-cosmic http://archive.ubuntu.com/ubuntu
  [...]
  W: Failure while configuring base packages.  This will be re-attempted up to five times.
  W: See /build-cosmic/debootstrap/debootstrap.log for details (possibly the package rsyslog is at fault)
  I: Configuring rsyslog...
  W: Failure while configuring base packages.  This will be re-attempted up to five times.
  W: See /build-cosmic/debootstrap/debootstrap.log for details (possibly the package rsyslog is at fault)
  W: Failure while configuring base packages.  This will be re-attempted up to five times.
  W: See /build-cosmic/debootstrap/debootstrap.log for details (possibly the package rsyslog is at fault)
  W: Failure while configuring base packages.  This will be re-attempted up to five times.
  W: See /build-cosmic/debootstrap/debootstrap.log for details (possibly the package rsyslog is at fault)
  W: Failure while configuring base packages.  This will be re-attempted up to five times.
  W: See /build-cosmic/debootstrap/debootstrap.log for details (possibly the package rsyslog is at fault)

I understand that it may be tempting to write this off as an Ubuntu bug
(and by the time you try to reproduce this it may well be that rsyslog
has been changed to work around this), but I don't think it is.
Bootstrapping Debian sid seems to work OK, but I think that's just luck.

The problem appears to be that setup_proc detects that it's running
inside a LXC container (actually LXD in this case, but it's still
container=lxc) and decides that this means that it doesn't need to mount
/proc or /sys; I think the original problem was perhaps that it couldn't
mount them due to lack of permissions.  The original history seems to be
from #731802, in which the second stage was being run inside LXC and the
container environment had already mounted /proc, or something like that.

But the fix for that problem isn't correct in this case.  debootstrap
happens to be running inside a LXD container, sure, but we aren't using
separate first and second stages, so the container environment clearly
can't be responsible for mounting /proc and /sys inside the
newly-created chroot.

At minimum, I'd suggest that the special handling for container
environments should be restricted to the case where debootstrap is
running with a separate second stage.

Furthermore, I'd have thought that, even if debootstrap is running with
a separate second stage inside a LXC/LXD container, it should at least
still check whether /proc and /sys are mounted and mount them if they
aren't, rather than assuming that they must be mounted.

Thanks,

-- 
Colin Watson                                       [cjwatson@ubuntu.com]